We can read in the book of Acts after the descent of the Holy Spirit and Peter’s speech that 3,000 souls were added to the Church.  They became members of the Church through a visible sacrament- Holy Baptism. They continued as members of the visible reality of the Church with a specific doctrine, sacramental, and prayer life. We can read  “And they continued steadfastly in the apostles' doctrine and in the communion, in the breaking of bread, and in the prayers. (Act 2:42 )”  The word for communion in the Greek is “κοινωνίᾳ”. (Act 2:42 BYZ)  It is the same word St. Paul uses for the Holy Communion of the Lord’s body and blood that we partake of each Sunday.  “The cup of blessing which we bless, is it not the communion of the blood of Christ? The bread which we break, is it not the communion of the body of Christ?  For we, though many, are one bread and one body; for we all partake of that one bread.(1Co 10:16-17 NKJ)” Just as the Lord’s body was visible and could be touched after the Resurrection, so the Church remains a visible body of believers.  This body, as we can see from the above verse from St. Paul’s letter to the Corinthians, is constituted by the “communion”, that is the breaking of the bread and the prayers. These were not just any prayers- but in the Greek, the definite article  ταῖς προσευχαῖς indicates specific liturgical prayers. These liturgical prayers have grown in length and in content over the years, however the Divine Liturgy today in the Orthodox Church is unchanged from the same basic shape and meaning of her earliest Apostolic liturgies.